Fix bugs in try*/catch*

Wasn't pushing Env, so wasn't releasing correctly.
Resulted in errors when in nested expressions.

Catch was also not popping the exception handler,
so repeated exceptions would not be handled correctly.

nasm/stepA_mal.asm

@@ -1732,6 +1732,7 @@ eval:
         
         push R9
         push R10
+        push r15                ; Env
         
         ; Set the error handler
         mov rsi, rsp            ; Stack pointer
@@ -1749,8 +1750,10 @@ eval:
         call incref_object      ; AST released by eval
         
         call eval
+        
         mov r8, rax             ; Result in R8
         
+        pop r15                 ; Environment
         ; Discard B and C
         ;add rsi, 8             ; pop R10 and R9
         pop r10
@@ -1766,6 +1769,11 @@ eval:
         ; Value thrown in RSI
         ;
 
+        push rsi
+        call error_handler_pop
+        pop rsi
+
+        pop r15                 ; Env
         pop r12                 ; B (symbol to bind)
         pop r13                 ; C (form to evaluate)
 
@@ -1800,7 +1808,9 @@ eval:
         mov rsi, [r13 + Cons.car] ; Form to evaluate
         call incref_object      ; will be released
 
+        push r15
         call eval
+        pop r15
         
         jmp .return